Calotropis procera (Asclepiadaceae) is one of the traditionally used antifertility plants in Nigeria.
Previous studies have shown that this antifertility plant has abortifacient property but none of them has reported
its possible biochemical mechanism of action. Organ bath experiments using cumulative doses of the extract
on rat uterine rings in Dejalonís solution aerated with 95% O2 + 5% CO2 produced an increase in tension (%
response) with an EC50 value of 0.1064 mg/mL. Blocking muscarinic receptors with 35 μg/mL atropine caused
the dose-response curve to slightly shift to the right (EC50 shift = 0.1064-0.1242), with a significant (p<0.05)
decrease in maximal tension (%response). However, the β2-adrenergic blocker (1 μM propanolol) caused a twofold
shift in the dose-response curve (EC50 shift = 0.1064-0.2591). The extract also exhibited its effect on cAMP
modulation of β2-adrenergic receptors by causing a significant (p<0.05) decrease in cAMP level after treatment
of cultured uterine cells with the extract. In conclusion, this study suggests that pet-ether extract of Calotropis
procera (Asclepiadaceae) may exerts its abortifacient effect by inducing myometrial contractions of the uterus
by binding to β2-adrenergic receptors thereby causing a decrease in the level of cAMP. cAMP reduction reduces
the activation of Protein Kinase A (PKA) thereby preventing PKA from inactivating Myosin Light Chain
Kinase (MLCK).